This invention relates to a valve lifter mounted in a direct type valve drive assembly for opening the valve by directly pushing down the valve with a rotating cam.
An ordinary valve driving assembly for directly pushing down an intake or exhaust valve with a rotating cam includes a valve lifter mounted between the cam and a valve stem. The valve lifter is pressed against the cam by the force of a valve spring which is mounted to the valve stem. Thus, the valve stem is pushed down by the cam through the valve lifter when the valve lifter is pushed down by contact with the cam.
Such a valve lifter is disclosed in unexamined Japanese utility model publication 3-8603. This valve lifter includes a guide cap mounted between the cam and the valve and has a closed end plate, a nut member in contact with the bottom surface of the closed end plate, an adjusting bolt threadedly engaged in the nut member, an engaging plate mounted on the bottom end of the adjusting bolt, and a return spring acting on the adjusting bolt to urge the bolt in the protruding direction and press its bottom end against the valve stem.
The guide cap is formed with a pin hole through which is inserted a pin. The pin is also inserted in a groove formed in the engaging plate near its outer edge to keep the adjusting bolt pushed in.
With this valve lifter, when the pin is pulled out with the valve lifter mounted between the cam and the valve stem, the adjusting bolt will protrude under the force of the return spring until it abuts the top end of the valve stem. In this state, no gap is present between the cam and the valve stem. Thus, this valve lifter can be easily mounted.
If the distance between the top ends of the cam and the valve stem changes due e.g. to temperature fluctuation, the adjusting bolt moves axially while rotating under the force of the return spring to absorb the change in distance. The valve can thus be opened and closed with high accuracy.
With this type of valve lifter, the guide cap and the nut member are separate members. This valve lifter further needs the engaging plate to transmit the spring force to the adjusting bolt. The number of parts is thus large. Therefore, a valve lifter that is lower in cost and easier to assemble is desired.
Further, since the adjusting bolt is threadedly engaged in the nut member in contact with the bottom surface of the closed end plate of the guide cap, the distance between the cam contact surface of the guide cap and the lower end of the adjusting bolt is long. Therefore, the axial length of the valve driving assembly is large. Thus, a more compact valve driving assembly is desired.
An object of this invention is to provide a valve lifter which is made up of a smaller number of parts and thus compact.